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re: watts???
16 apr 1999
clare snyder wrote:
> wrote:
>>i have a fan that uses 0.5 amps @ 115 vac. don't i say .5 amps x
>>115 volts = 57.5 watts...
>your fan consumes .5*115=57.5 va of power.
that's apparent power, ie real power combined with "volt-amperes reactive."
the fan probably consumes less real power in watts than that,
eg 46 real watts, if the power factor were 0.8.
>your battery is rated at 120 amp hours, at 12 volts - or 12*120=1440
>watt hours. if your inverter was 100% efficient you could run the fan
>1440/57.5=25.04
i'd say you could run the fan for 1440wh/46w = 31.3 hours. the units
give clues in these calculations: wh/w = h. dividing watt-hours by
volt-amperes doesn't make much sense in the ac world.
>the dc fan move 14 cfm/watt, where the ac fan moves only 7...
large slow fans are more efficient. my favorite ac fans are grainger's
4c688 10" 36 watt 560 cfm (15.6 cfm/w) fan with a 149 f upper operating
temperature limit and their 48" 86 watt 21k cfm (244 cfm/w) 4c853 315 rpm
ceiling fan, which has a power factor of 86w/(120vx0.85a) = 0.84.
nick
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